I can't say anything about a Golf, but I frequently rent new Jettas (gasoline) when I travel for work. I'm not a huge fan of them. You can compare my description to that of your Golf and see what you think.
The 2.5L is nice and sporty. It doesn't feel like it has a WHOLE lot more than the 2.0L in the Focus, though. One thing that is consistent in the Jetta, and that I absolutely hate, is that you have to almost bury your foot in the accelerator to get the car to do anything but crawl off the line in first gear. 2nd gear will throw you into your seat, though. It feels like the car is trying to protect itself and won't give it fuel or something.
The interior seems kind of cheap. When tapping on the doors they sound very hollow, and the material feels a lot like plastic. That isn't to say that the Focus doesn't have plastic door panels, but they feel much more substantial. The full metal door handles in the Focus are nice, too.
The seats are more comfortable than the Focus, but I'm not a fan of the pleather they use. Cloth or real leather and they should be nice. I find the Focus leather seats to be VERY uncomfortable (my only major gripe with the car).
I've never owned a MT, but I wish I had purchased one for the Focus. The DCT isn't awful, but I don't drive in D. I'm always using S manumatic. The transmission seems to shift better, is more reliable, and doesn't slip the clutch like mad after 1st gear.
Your gas mileage will vary very heavily based on where and how you drive. When I first purchased my Focus I was getting about 38mpg with about 3/4 highway, and very easy accelleration. Now I get between 30 and 33 with a heavier foot and only about 1/4 highway miles. I have a Titanium with 18" wheels.
I like the hand brake in the 2013 Jetta. Feels much smoother. The Focus hand brake definitely works, but it feels like the increments for tightening the brake (clicks) are more spread out.
When I get on it in the Focus I have yet to experience torque steer, though I hear the ST has a bit of a problem with it. The Jettas have been hit and miss (2011 - 2013).
The last nice thing you will get if you decide to go with a Focus is that the displays in the car are much nicer than what I've seen in the Jetta. You get full color LCDs instead of the monochromatic screens.
Hope this helps.